Gas turbine engine compressors often include air inlet systems with heating devices for raising the temperature of the incoming air stream. Compressor IGV icing, surge/stall, combustion lean blowout, and the like may result due to cold ambient conditions and/or due to other types of operating parameters. As such, the compressor pressure ratio may be accommodated by bleeding an amount of compressor discharge air and recirculating the air back to the compressor inlet. Mixing the cooler ambient air with the bleed portion of the hot compressor discharge air reduces the air density and the mass flow to the gas turbine. Current inlet bleed heat systems may use impingement holes for air injection in a direction perpendicular to the main airflow direction. Other known inlet heat bleed systems may use acoustical nozzles in a filter house transition section for injection in the airflow direction. Many other types of inlet bleed heat control systems and methods of bleed injection also may be used.
Although these known inlet bled heat control systems may be adequate for heating the incoming airstream into the compressor, the nozzles and the piping usually involved in injecting the bleed air may disrupt the incoming airflow so as to result in an increase in the pressure drop thereacross. This interference may have an impact on overall gas turbine operation and efficiency when the inlet bled heat system is operational.
There is thus a desire for an improved inlet bleed heat system for a gas turbine engine. Preferably such an improved bleed heat system may adequately heat the incoming airflow with a reduced the pressure drop thereacross so as to provide temperature and flow uniformity while complying with relevant noise limitations and other operational parameters.